Numerous systems have been devised for vehicle guidance which range from fully automatic steering or speed control to merely providing roadway information to the driver such as an electronic warning of upcoming road conditions such as a difficult curve, etc. Many of them involve the implantation of magnetic strips into a road surface such as U.S. Pat. No. 3,085,646 issued to Paufve and U.S. Pat. No. 3,575,255 issued to Wickstrom for automatic speed and directional control of a vehicle. A number of other related systems are cited in U.S. Pat. No. 4,003,445 issued to De Bruine. My U.S. Pat. No. 3,837,756 discloses mixing ferric particles and optically reflective material with concrete to produce a magnetizable road surface.
Although systems have been proposed for vehicle guidance using magnetic fields within the road surface, there exists a need for an inexpensive and simple means for impressing a magnetic field onto a road surface and a means to alter the magnetic field at a future time without tearing up the roadway. In addition, a simple means for producing an alternative magnetic field pattern in the roadway to signal a change in the vehicle speed limit due to changing road conditions such as curves, urban congestion or road construction ahead is needed.
The present invention provides means for impressing a plurality of magnetic field patterns into magnetizable road surfaces material while or after it has been laid and provides a simple means for altering the magnetic pattern at any time in the future.